After a week of rewriting a core idea, and after going through a few pages of feedback, I'm back here.

previous core idea was "vest that does X once conditions are met". I've scrapped that.
Next core idea was "Man that trades disease with vest and cigarette". I'm dialing that back by a bit.

My problem is though, I really want to work with this idea, regardless if it's somewhat similar to SCP-353, because the man that I was thinking about, rather takes major diseases onto himself to be good etc.

One of the challenges you're going to face is that, at the moment, your concept is "an item that does a weird thing." While writing such an SCP isn't impossible, it isn't easy. There needs to be something that makes your reader interested in your concept. You want to leave them with something, be it a feeling or a thought. Some SCPs do this by being so absurdly and interestingly weird that they can get away with being a thing that does X, however, most SCPs, especially the recent ones, include a narrative or hook to make the item more appealing to the reader.

I would advise pursuing one of these two roots. The first root is to question your idea. Where did this come from? Why would it make a good SCP? What would a reader think once they read it? This can be helpful, as it can let you construct a narrative. However, you run the risk of forming a story around an item when that item isn't really essential to the story. The second option involves going a little further back in the process. It doesn't mean scrapping the idea, but it means thinking about what sort of influence you want your draft to have. Look for your motivation for the idea before you get caught up in the idea itself. Don't start with "Vest that does X," start with the person who wore the vest and let the item change to fit that idea.